VLAN Trunking Protocol (VTP)
VTP is a protocol that runs over trunk links and synchronizes the VLAN
databases of all switches in the VTP domain. A VTP domain is an administrative
group—all switches within that group must have the same VTP
domain name configured or they do not synchronize databases.
VTP works by using Configuration Revision numbers and VTP advertisements:
■ All switches send out VTP advertisements every five minutes, or when
there is a change to the VLAN database (when a VLAN is created,
deleted, or renamed).
■ VTP advertisements contain a Configuration Revision number. This
number is increased by one for every VLAN change.
■ When a switch receives a VTP advertisement, it compares the
Configuration Revision number against the one in its VLAN database.
■ If the new number is higher, the switch overwrites its database with the
new VLAN information, and forwards the information to its neighbor
switches.
■ If the number is the same, the switch ignores the advertisement.
■ If the new number is lower, the switch replies with the more up-to-date
information contained in its own database .